1. Field of the Invention
The present invention relates to an X-ray CT scanner for collecting X-ray projection data with respect to a patient to be examined.
2. Description of the Related Art
In general, a conventional X-ray CT scanner comprises: an X-ray tube for radiating a flat, fan-shaped X-ray beam; and an X-ray detector arranged in opposition to the X-ray tube for the detection of the X-ray beam. The patient is placed between the X-ray tube and the X-ray detector, and the X-ray tube and the X-ray detector are rotated in the same direction and at the same angular velocity, with the patient as the center of rotation. During the rotation of the patient, X-ray projection data representing various-direction images of the patient is collected on the basis of the X-rays detected by the X-ray detector. After the X-ray projection data is collected in a sufficient amount, it is analyzed by a computer to calculate the X-ray absorption rate at each point of a slicing plane of the patient. In accordance with the calculated X-ray absorption rate, gradation data is provided for the collected X-ray projection data, for reconstruction of a slice image of the patient.
The CT scanner mentioned above employs either a cable or a slip ring mechanism, so as to transmit the X-ray projection data on real time from a rotatable frame portion (on which the X-ray tube and X-ray detector is supported) to a stationary frame portion. In the case where the cable is employed, a cable-handling apparatus such as that disclosed in U.S. Pat. No. 4,646,333 is required to extend or wind the cable, since the cable must be long enough not to prevent rotation of the rotatable frame portion. The use of the slip ring mechanism is disclosed in U.S. Pat. No. 4,093,859, wherein a contact brush and an annular contact are used for data transmission between the rotatable frame portion and the stationary frame portion.
As mentioned above, a conventional CT scanner apparatus employs either a cable-handling device or a slip ring mechanism. However, a CT scanner apparatus employing the cable-handling device is inevitably large as a whole since the cable-handling device occupies a wide installation space. On the other hand, the CT scanner apparatus employing a slip ring mechanism requires a high manufacturing cost since the slip ring mechanism is complex.